Method and apparatus for piercing thin sheet material

ABSTRACT

A method and apparatus for piercing thin sheet material, such as plastic film, is provided wherein the sheet material is passed between a piercing member having a plurality of independently resilient protrusions extending therefrom and a backing member having a retiform exterior surface, said piercing member or said backup member being moved relative to the other member, thereby causing said resilient protrusions to follow said retiform surface and selectively pierce said film.

United States Patent 1 Clash et a].

[ Oct. 2, 1973 METHOD AND APPARATUS FOR PIERCING THIN SHEET MATERIAL[75] Inventors: David Guernsey Clash, Fairview Park, Ohio; TheodoreFrederick Kozak, Peekskill, NY.

[73] Assignee: Union Carbide Corporation, New

York, N.Y.

[22] Filed: Oct. 20, 1971 [21] Appl. No.: 190,908

[52] US. Cl 83/309, 83/348, 83/660,

83/678 [51] Int. Cl. B26f 1/18, B27f 1/24 [58] Field of Search 83/30, 2,349, 309,

83/542, 678, 660, 348; 264/154, 156, DlG. 47, DIG. 70; 225/93, 97

[56] References Cited UNITED STATES PATENTS 2,980,982 4/1961 Costa et a1225/97 X l l DRIVE MECHANISM 2,870,840 1/1959 Kwitek 83/678 X PrimaryExaminer.l. M. Meister Attorney-John F. Hohmann et a1.

[57] ABSTRACT A method and apparatus for piercing thin sheet material,such as plastic film, is provided wherein the sheet material is passedbetween a piercing member having a plurality of independently resilientprotrusions extending therefrom and a backing member having a retiformexterior surface, said piercing member or said backup member being movedrelative to the other member, thereby causing said resilient protrusionsto follow said retiform surface and selectively pierce said film.

10 Claims, 7 Drawing Figures PATENTEI] 081 21975 MECHANISM SHEET 1 BF 2L DRIVE FIG.

FIG.

FL-ITITT iTlTi i rri LTT +1- INVENTORS DAVID G. CLASH THEODORE F KOZAKATTORNE PAIENTED 0m 2875 SHEET 2 BF 2 METHOD AND APPARATUS FOR PIERCINGTHIN SHEET MATERIAL The present invention relates to a method andapparatus for piercing thin sheet material and more particularly relatesto a method and apparatus for introducing a plurality of small, closelyspaced slits in sheet material.

As used herein and in the appended claims, the terms film, sheet,membrane or foil refer, unless a specific composition is specified, toany thin, relatively flat self-supporting material such as plastic orrubber film, paper, metal foil, and the like having a thickness of 0.25to mils.

It is well known that for many uses it is desirable or necessary tointroduce a plurality of apertures into a film which might otherwise besubstantially water or air impermeable. Examples of such uses includepuncturing refuse bags to speed degradation of the bag contents,puncturing packaging materials where trapped air is a problem,puncturing dry cleaning bags to render them safe to children, andfabricating breathable plastic films for use in place of nonwovens inuses such as disposable hospital linens, and the like.

One use which could employ a plurality of perforations in two distinctparts of the same product is a surgical dressing or bandage.Plastic-backed adhesive bandages have for some time employed a pluralityof holes in the portion of the plastic backing adjacent to the absorbentdressing. Such holes provide ventilation to per mit aeration of thewound. More recently, small strips of thermoplastic film have beenprovided on the side of the absorbent dressing which is positionedadjacent to the wound. Absorbent dressings, which have traditionallybeen fibrous materials, tend to stick to a wound upon healing andtearing away such a dressing can reopen a partially healed wound uponremoval of the bandage. The use of a thermoplastic film adjacent to thewound greatly decreases the possibility of the bandage sticking to thewound and therefore promotes easy removal of the bandage from the wound.In order to permit the secretions from the open wound to reach theabsorbent dressing it has been necessay to provide the thermoplasticfilm with apertures very similar to the ventilation holes formed in theplastic backing of the bandage. Perforate dressings of this type aredescribed, for example, in US. Pat. No. 3,543,750.

Copending U. S. application Ser. No. 73,185 filed Sept. 17 1970discloses yet another use for a thermoplastic sheet having a pluralityof perforations therein. A disposable baby diaper construction isdisclosed which employs, as the layer adjacent to the body of the baby,a thermoplastic film having a plurality of valvular openings thereinwhich permit passage of urine from the baby to an absorbent backingmaterial while retarding flow in the opposite direction. The skin of thebaby is thereby kept drier than has heretofore been possible.

It has previously been suggested to manufacture perforate films throughthe use of punching dies or by localized heating of thermoplastic filmsthrough the use of heated pins, dielectric methods or heated gases. Morerecently it has been suggested that the film be initially cast from anorganosol onto an open-mesh grid pattern such that the resulting filmwill have preformed holes or incorporating into the film a solublepowder which is subsequently dissolved.

Each of these methods is subject to one or more disadvantages in usesuch as wasted material in dye punching and using soluble materialsincreased processing time in heating or high cost for heating orpreforming holes.

It is an object of the present invention to provide a simple method andapparatus for piercing films.

It is a further object of the invention to provide an inexpensive andefficient apparatus for the piercing of films which aparatus can beadapted to accommodate various thicknesses of film and which can bereadily modified to change the size, shape, and placement of theperforations.

It is a further object to provide a method and apparatus for introducingvalvular openings into an otherwise liquid impermeable thermoplasticfilm.

These and other objects are accomplished by a method and apparatus forperforating films employing the passage of the film between a piercingmember having a plurality of protrusions extending therefrom and abackup member having a retiform exterior surface against which theprotrusions are resiliently held.

The apparatus of the invention comprises only four basic components: apiercing member, a backup memher, a drive means to impart relativemotion between said piercing member and said backup member, and meansurging said piercing member and said backup member into adjacency.

The backup member should have a retiform exterior surface, which, asused herein and in the appended claims, means that it should have highand low portions or hills and valleys when viewed in cross-section.Preferably, the surface will be undulant, such as that of a woven wirescreen, but to be operative it is necessary only that parts of thesurface of the backup member be either higher or lower than the medianplane of the surface of the member.

The piercing member should comprise a plurality of resilient protrusionssuch as a comb having a plurality of independently resilient teeth.

The invention will be more particularly described with reference to theaccompanying drawings in which:

FIG. 1 is a diagrammatic side elevational view of an apparatus inaccordance with the present invention;

FIG. 2 is a perspective view of the piercing memberbackup membercombination of FIG. 1 with the film removed for the purpose of betterillustrating the apparatus;

FIG. 2a is an enlarged view of section 2a of FIG. 2; and

FIG. 3 is a perspective view of a film slit by the apparatus of FIG. 1.

FIG. 4 is an alternate embodiement wherein the backup member is in theform of an endless belt;

FIG. 5 is an alternate embodiement wherein the piercing member is in theform of a comb;

FIG. 6 is an alternate embodiement wherein the piercing member is in theform of a wire brush.

Referring in detail to the drawings there is shown an apparatus forpiercing film such as a thermoplastic film 10 by passing the filmbetween a piercing member 12 and a backup roll 14 which will each bedescribed in greater detail hereinafter.

Thermoplastic film 10 may be supplied to the apparatus of the inventiondirectly from an extruder or from a supply roll, not shown. The film ispositively carried through the apparatus by being passed between the nipof the backup roll 14, which is driven in a clock-wise direction by amotor 11 through a drive mechanism 13, and a pressure roll 16. A pair ofnip rolls 18, 20 and an idler roller 22 control the tension of the filmsas it is being passed between the piercing member 12 and the backup roll14.

The backup roll 14, in the embodiment of the invention shown in FIGS. 2and 2a, is a 6 inch diameter steel drum 24 having a stainless steel wirescreen 26 encircling the central portion of its outer circumference.

The piercing member 12 of FIGS. 2 and 2a is a strip of tempered springsteel having a plurality of parallel slits 28 cut therein to formresilient ribs 30 extending from a continuous steel backbone 32. Thebackbone 32 is secured in a holder 34 which is supported by the frame(not shown) of the apparatus and is adjustable to control the contactangle and contact pressure between the ribs 30 and the wire screen 26.

As the backup roll 14 movesthe film under the piercing member 12,resilient ribs 30 individually follow the undulations of the wire screen26. The film is perforated when the ribs pass over raised portions ofthe screen, since the film is tightly pressed against the wire by themetal edges of the ribs. When the ribs contact the valley portions ofthe screen, the contact pressure between the ribs and the wire isgreatly reduced and the film is not pierced by the ribs. The resultingpierced film 36 will have perforations 38 (FIG. 3)

which correspond to each of the raised portions of the wire screen. Ifthe film is wider than the wire screen 26, unperforated borders 40, 42will be formed along the sides of the film. The same result is achievedif the piercing member 12 is narrower than the wire screen 26.

Using a 10 inch wide, 9 X 9 mesh screen formed from 0.023 inch stainlesssteel wire secured to a inch wide, 6 inch diameter drum which wasrotated at a speed, measured at the circumference of the drum, of 54feet per minute the 10 inch central portion of a one mil polyethylenefilm measuring 14.5 inches in width was continuously pierced by apiercing member formed by cutting 1.5 inch deep slits in a strip oftempered spring steel 10 inches wide and 0.010 inch thick. The slitswere spaced 0.17 inch apart and formed a piercing member which consistedof a continuous backbone having 54 resilient ribs extending therefrom.The resulting pierced film contained uniform slits of a pattern similarto that shown in FIG. 3 of the drawings.

In operation, the retiform surface of the backup member acts as a seriesof camming tracks for the protrusions of the piercing member. Thesupport for the piercing member is arranged in a manner such that, uponrelative longitudinal movement between the piercing member and thebackup member, the individual protrusions of the piercing member trackthe surface of the backup member. Due to their resiliency theprotrusions follow the hills and valleys of the backup member exertinggreater force against the hills than against the valleys. When a film ispositioned between the piercing member and the backup member during thistracking, the film is selectively perforated with the portions of thefilm covering the hills being perforated while the portions covering thevalleys remain unperforated.

From the above it will be obvious to those skilled in the art thatvarious combinations of piercing members and backup members can be. usedto obtain a wide variety of film aperture sizes, shapes and patternswithin the scope of the present invention, and that by modifying themesh or type of screen used and placement or size of ribs in thepiercing member the apparatus of the present invention can be used toform various perforation patterns in different types and thicknesses offilm. Variations in speed of piercing, the angle of and pressure exertedby the piercing member, and drawing the film from the piercing zoneunder tension will all be useful tools in obtaining preferred films inaccordance with the present invention for particular uses.

Referring to the types of piercing members useful in the apparatus ofthe present invention, it will be apparent to those skilled in the artthat various materials can be substituted for the slit spring steelmember described above. For example, spring steel ribs welded to abackbone, a wire brush 58, as shown in FIG. 6, or even razor blades willbe useful in combination with various backup rolls to obtain a varietyof perforation patterns. A comb 56, as shown in FIG. 5, comprising abackbone having a plurality of teeth extending therefrom will also beuseful. Likewise, the ends of the ribs or teeth of the piercing membermay be sharpened, pointed, flattened, rounded or separated to obtainvarious piercing effects.

The backup roll will also be susceptible to change to accommodate thevarious types of piercing members and obtain different perforationpatterns. The retiform surface may be provided by embossing, etching,knurling or perforating a metal sheet or roll and the backup member maybe in the form of a continuous belt 52, as shown in FIG. 4, passingaround rollers 48 and 50 rather than the roll described or a screen ormetal sheet secured to continuous belt or roll.

Likewise, from the above it will be obvious that while the presentinvention has been set forth in some detail and described withparticularlity, it is susceptible to changes, modifications andalterations without departing from the scope and spirit of theinvention.

What is claimed:

1. An apparatus for introducing a plurality of apertures in a filmcomprising a piercing member having a plurality of independentlyresilient protrusions extending therefrom, a backup member having aretiform exterior surface constituting camming tracks for saidprotrusions, support means for said piercing member, means to impartrelative motion between said backup member and said piercing member, andmeans urging said piercing member and said backup member into adjacencythereby causing said protrusions to track in said camming tracks duringrelative motion between said piercing member and said backup member.

2. The apparatus in accordance with claim 1 wherein said piercing memberis a metal comb.

3. The apparatus in accordance with claim 1 wherein said piercing memberis a wire brush.

4. The apparatus in accordance with claim 1 wherein said piercing memberis a metal strip having a plurality of substantially parallel slitsextending from one edge thereof in the direction of the opposite edgethereby defining said protrusions.

5. The apparatus in accordance with claim 1 wherein said backup memberhas an undulant exterior surface.

6. The apparatus in accordance with claim 1 wherein said backup memberis a wire screen.

7. The apparatus in accordance with claim 1 wherein said backup memberis in the form of an endless belt teeth extending therefrom, a backupmember which is a wire screen secured to a drum, drive means incombination with said drum to rotate said drum relative to said piercingmember, and support means for said piercing member maintaining at leasta plurality of the teeth of said piercing member in adjacency with saidscreen such that said teeth will individually track the undulations ofsaid screen during rotation of said drum and selectively perforate afilm positioned on said drum.

10. A method of introducing a plurality of apertures in a filmcomprising supplying said film to a perforating area, passing said filmbetween the nip of a plurality of resilient teeth and a retiform surfaceagainst which said teeth are held in adjacency at said perforating areaand moving said film through said perforating area in a manner such thatsaid teeth follow said retiform surface perforating said film when theteeth engage the higher portions of said surface and allowing said filmto pass unperforated when the teeth engage the lower portions of saidsurface.

1. An apparatus for introducing a plurality of apertures in a filmcomprising a piercing member having a plurality of independentlyresilient protrusions extending therefrom, a backup member having aretiform exterior surface constituting camming tracks for saidprotrusions, support means for said piercing member, means to impartrelative motion between said backup member and said piercing member, andmeans urging said piercing member and said backup member into adjacencythereby causing said protrusions to track in said camming tracks duringrelative motion between said piercing member and said backup member. 2.The apparatus in accordance with claim 1 wherein said piercing member isa metal comb.
 3. The apparatus in accordance with claim 1 wherein saidpiercing member is a wire brush.
 4. The apparatus in accordance withclaim 1 wherein said piercing member is a metal strip having a pluralityof substantially parallel slits extending from one edge thereof in thedirection of the opposite edge thereby defining said protrusions.
 5. Theapparatus in accordance with claim 1 wherein said backup member has anundulant exterior surface.
 6. The apparatus in accordance with claim 1wherein said backup member is a wire screen.
 7. The apparatus inaccordance with claim 1 wherein said backup member is in the form of anendless belt which is driven longitudinally with respect to saidpiercing member.
 8. The apparatus in accordance with claim 1 whereinsaid backup member is secured to a rotatable drum.
 9. An apparatus forintroducing a plurality of apertures in a thermoplastic film comprisinga piercing member having a plurality of independently resilient teethextending therefrom, a backup member which is a wire screen secured to adrum, drive means in combination with said drum to rotate said drumrelative to said piercing member, and support means for said piercingmember maintaining at least a plurality of the teeth of said piercingmember in adjacency with said screen such that said teeth willindividually track the undulations of said screen during rotation ofsaid drum and selectively perforate a film positioned on said drum. 10.A method of introducing a plurality of apertures in a film comprisingsupplying said film to a perforating area, passing said film between thenip of a plurality of resilient teeth and a retiform surface againstwhich said teeth are held in adjacency at said perforating area andmoving said film through said perforating area in a manner such thatsaid teeth follow said retiform surface perforating said film when theteeth engage the higher portions of said surface anD allowing said filmto pass unperforated when the teeth engage the lower portions of saidsurface.